1. Field of the Invention
This invention relates generally to pyrometers and more particularly to a pyrometer system using a dual optical path method for comparing long and short wavelengths of light emitted by a radiating object or moving stream of particles and a sensor used to image two images side-by-side.
2. Description of Related Art
The following art defines the present state of this field:
Tagami, U.S. Pat. No. 4,411,519 describes methods and systems for measuring the temperature and spectral factors of a number of specimens (or radiators). The radiant fluxes from the specimens are spectrally analyzed with respect to effective wavelengths from M different channels (M being greater than or equal to 3). A relation among the spectral radiant flux intensity, approximated spectral factor (depending only on wavelength) and the temperature is determined for each channel by using Planck's radiation law with the condition that a relation N+K=M is kept among M of the number of channels, N of the number of specimens with unknown temperature values and K of the number of unknown terms of the approximated spectral factors of the specimens. Strict algebraic development of such relation is employed to cancel out all of the unknown terms of the spectral factor to obtain a one-dimensional equation concerning the sole temperature. Such equation is solved to determined the temperature of the specimens, and the spectral factor of the specimens, and the spectral factor of the specimens is obtained from the determined temperature values.
Tatsuwaki et al., U. S. Pat. No. 4,413,324 describes a temperature pattern distribution measuring method and apparatus by which portions of light from parts of an area of an object whose temperature distribution patterns is to be measured, and whose parts are in a predetermined pattern, are passed through first and second optical filters which respectively pass different wavelengths of light. The level of energy passed by the respective filters for the respective portions of light are determined by scanning the light from the filters with a pickup device or devices and, by using the determined energy levels. An arithmetic unit carries out a two-color temperature determining operation for determining the temperature on each part of the area of the object. The temperature pattern of the area of the object can thereby be determined from the temperatures of the parts of the area.
Lillquist et al., U.S. Pat. No. 4,656,331 describes a multi-purpose optical sensor that operates in the medium-to-far infrared wavelength spectral region to sense the surface temperature of plasma-jet spray coating material. This plasma itself emits little or no radiation in this region and, accordingly, the output signal from the sensor is used to adjust the electrical input and other variables associated with the plasma spray torch to insure that particles arriving at the substrate surface to be coated are, in fact, in a molten state. The sensor employs infrared filters and, additionally, the sensor is used to monitor not only coating and temperature but also plasma beam divergence and particle seeding density to provide other control functions.
Lillquist, U.S. Pat. No. 4,687,344 describes an imaging radiometer for high temperature measurements that has a sensor head comprised of a solid-state video camera operated in a fixed gain mode, preferably one with a charge injection device detector, an infrared filter, and a lens system to image a radiating object on the detector array. Spectral response of the system is limited to 700 to 1100 nanometers or a smaller portion of this near-infrared band. The video signal output of the sensor is processed and object temperature is displayed on a television monitor, alternatively the video signal is presented to a digital frame grabber and converted to a temperature map.
Moreau et al., U.S. Pat. No. 5,180,921 describes a method and an apparatus for monitoring simultaneously the temperature and the velocity of sprayed particles. The system is comprised of a sensor head attached to the spray gun, and optical fiber transmitting the collected radiation to detection apparatus, and a protective detection cabinet incorporating two detectors. A two-slit or multiple-slit, mask is located in the sensor head at the end of the optical fiber. For the temperature measurements, the emitted radiation is collected by the sensor head, transmitted to two photodetectors, and filtered by interference filters at two adjacent wavelengths. The particle temperature may be computed from the ratio of the detector outputs. To measure the velocity, the two-slit system collects radiation emitted by the in-flight particles travelling in the sensor's field of view, which generates a double peak light pulse transmitted through the optical fiber. The time delay between these two peaks may be evaluated automatically and the particle velocity computed knowing the distance between the two slit images.
Carter et al., U.S. Pat. No. 5,225,883 describes an apparatus and method for providing a real-time video display and a temperature map display of an object, in particular a flame, comprises a single CCD video camera and optical equipment which focuses separate light bundles onto a photosensitive surface of the camera. A separate band pass filter is used in each light bundle to filter selected different wavelengths of light. The video signal from the camera is used in a video digitizer to obtain data, which can be used to calculate a temperature map based on the different wavelengths of light of the two bundles. The video signal is also used to produce a real-time video display of the object.
Kamiya et al., U.S. Pat. No. 5,337,081 describes a triple view imaging apparatus that is provided for measuring quantitative distribution of material or property in a sample. In the triple view imaging apparatus, an optical system receives an original optical image of the sample, separates the original optical image into at least two secondary optical images having different optical properties from one another, and projects the at least two secondary optical images at a single view angle. A single video camera simultaneously picks up the thus projected plurality of secondary optical images as a single composite image and produces image signals representing the light intensities of the plurality of secondary optical images. An image processor receives the image signals and processes the image signals to obtain final image signals representing a relationship between the image signals for respective ones of the plurality of secondary optical images. An image display receives the calculated final image signals and displays a tertiary optical image based on the calculated final image signals, which defines quantitative distribution of material or property in the sample.
The prior art apparatus and methods suffer from important limitations. We find no provision or method step for matching the magnifications of the two images to the necessary level of precision for achieving the required accuracy of the method. The prior art does not teach how to control stray light at the detection plane. Stray light can be a major cause of error in the detection system. The prior art also fails to teach a means for presenting two images normally onto the detector surface so as to avoid distortion and foreshortening. If the images are not in focus across the entire detector field, both the accuracy and resolution of the temperature distribution will be degraded. Adjustment of angular and linear registration of dual images to the precision required to achieve high-resolution temperature readings is not taught. In the prior art, data processing steps are vague and do not include calibration. The prior art tends to teach the use of the Planck relationships directly, while in reality losses due to transmission efficiencies in each leg of a dual path system, and differences in sensitivity at the detector are significant and must be taken into account in any successful dual image process. The method of Moreau tends to be slow and have reliability problems, both of which are avoided in the present method. While the two-wavelength imaging pyrometers taught in the prior art use two synchronized imaging cameras, the current invention achieves similar optical performance but with the reduced size and cost and the simplicity of a single camera configuration. The present invention overcomes the limitations of the prior art by providing a beam joiner for improved dual image positioning correlation and normal beam ray directing and provides further related advantages as described in the following summary.